Conventional powder cosmetic products are typically in the form of a pressed powder cake. Compaction of the powder is necessary to provide sufficient physical cohesion so that the powder cosmetic products can be in the form of a portable compact desired by consumers. However, powder cakes tend to have weak structures because they generally do not incorporate a continuous structural component and are therefore poorly self-supporting. Notably, conventional powder cosmetic products (i.e., powder cakes) are fragile and tend to flake and/or crumble and readily break or crack upon impact. For example, the conventional product is likely to break or crack when dropped by a consumer, resulting in a loss of product usefulness. Traditionally, wet (esters and oils) and dry binders have been incorporated into pressed powders to allow for a stronger cake. However, these binders together with oils from the skin and pressure applied during normal use results in a glazing effect, which is the formation of glossy, hardened aggregates on the surface of the powder cosmetic product. Glazing reduces “payoff” of the powder cosmetic product such that the remaining powder cosmetic becomes essentially unusable by the consumer and is therefore wasted.
The conventional method of preparing a powder cosmetic product is by compressing cosmetic powders with a strong compressive force (e.g., 1000 psi or greater) to obtain pressed powders, or a powder cake. As a consequence of the strong compressive force required to obtain a powder cake, the pressed powders cannot incorporate pressure sensitive components, which would not withstand compaction and consequently lose their functionality.
Representative of the conventional approach to preparing pressed powdered cosmetics is JP Patent Publication 2004-217567, the disclosure of which is incorporated herein by reference. That publication describes a solid powdery eye shadow comprising (a) a powder, provided that the content of a plate-like powder in the whole powder is at least 70 mass % and that the content of flake-like salicylic anhydride in the whole plate-like powder is 5-80 mass %; (b) 1-10 mass % of a hydrocarbon wax powder; and (c) 10-20 mass % of an oily component which is pasty and/or liquid at room temperature. The solid powdery eye shadow is formed by pressing components (a)-(c) into a metal dish.
Alternatively, the ingredients of a powder cosmetic product can be mixed with a solvent and placed in a mold. The solvent is evaporated from the molded mixture to produce a powder cake. An example of an evaporated powder cake is described in U.S. Pat. No. 4,414,200 (“the '200 patent”), the disclosure of which is incorporated by reference. The '200 patent provides a powder stick composition for topical application produced by incorporating an active ingredient, a finely divided inert filler, and a fatty alcohol with siloxane to form a slurry. Thereafter, the slurry is molded and a major portion of the siloxane is evaporated from the cosmetic composition. However, because a shear force is required to blend the powder and solvent mixture, the pressed powders also cannot incorporate shear sensitive components. In addition, the evaporative process is lengthy and the use of certain solvents (e.g., water) can promote undesirable microbial growth.
There is a need in the art for powder cosmetic products that overcome one or more of the foregoing deficiencies of conventional powder cosmetic products and which provides products having heretofore unobtainable advantages. It is therefore an object of the invention to provide powder cosmetic products with improved physical strength so that unique 3-dimensional shapes of powder cake can be incorporated, while providing optimal payoff during use. It is a further object of the invention to provide powder cosmetic products with an improved useable life-span and resistance to glazing effects from repeated use. It is yet another object of the invention to provide powder cosmetic products capable of incorporating a broad range of functional ingredients such as pressure sensitive and/or shear sensitive components.